Reconfigurable Distributed Active Transformers

ABSTRACT

Reconfigurable distributed active transformers are provided. The exemplary embodiments provided allow changing of the effective number and configuration of the primary and secondary windings, where the distributed active transformer structures can be reconfigured dynamically to control the output power levels, allow operation at multiple frequency bands, maintain a high performance across multiple channels, and sustain desired characteristics across process, temperature and other environmental variations. Integration of the distributed active transformer power amplifiers and a low noise amplifier on a semiconductor substrate can also be provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to provisional U.S. Patent ApplicationSer. No. 60/363,424, filed Mar. 11, 2002, and Ser. No. 09/974,578, filedOct. 9, 2001 which are expressly incorporated by reference for allpurposes.

FIELD OF THE INVENTION

The present invention pertains to the field of distributed activetransformers. More specifically, the invention relates to distributedactive transformers that include features that provide additionalcontrol over operational parameters.

BACKGROUND OF THE INVENTION

A distributed active transformer includes a primary winding that usesactive devices to control the current direction and magnitude on thewinding. For example, U.S. patent application Ser. No. 09/974,578, filedOct. 9, 2001, describes distributed active transformers that cancomprise at least two push/pull amplifiers designed to amplify an RFinput signal. The distributed active transformer can be operated where afirst amplifier causes current to flow on the primary winding in a firstdirection, and where a second amplifier causes current to flow on theprimary in a second direction. In this manner, an alternating current isinduced on the secondary winding.

SUMMARY OF THE INVENTION

In accordance with the present invention, a distributed activetransformer is provided that overcomes known problems with existingtransformers.

In particular, a distributed active transformer is provided that allowssections of the distributed active transformer to be independentlycontrolled.

In accordance with an exemplary embodiment of the present invention, adistributed active transformer is provided. The distributed activetransformer includes a primary winding having two or more sets ofpush/pull amplifiers, where each set of push/pull amplifiers is used tocreate an alternating current on a section of the primary winding. Asecondary winding is disposed adjacent to the primary winding, such thatthe alternating current on the primary induces alternating current onthe secondary. The primary winding and the secondary winding can bedisposed on a semiconductor substrate.

The present invention provides many important technical advantages. Oneimportant technical advantage of the present invention is a distributedactive transformer that allows sections of the distributed activetransformer to be independently controlled, so as to adjust theoperating parameters of the distributed active transformer.

Those skilled in the art will appreciate the advantages and superiorfeatures of the invention together with other important aspects thereofon reading the detailed description that follows in conjunction with thedrawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagram of a distributed active transformer in accordancewith an exemplary embodiment of the present invention;

FIG. 2 is a diagram of a distributed active transformer with two primarywindings in accordance with an exemplary embodiment of the presentinvention;

FIGS. 3 and 3A are diagrams of a distributed active transformer withfirst and second primary windings and compensating capacitors inaccordance with an exemplary embodiment of the present invention;

FIG. 4 is a diagram of a distributed active transformer with first andsecond primary windings and compensating capacitors in accordance withanother exemplary embodiment of the present invention;

FIG. 5 is a diagram of a distributed active transformer with impedancetransformation ratio correction and resonance frequency selection inaccordance with an exemplary embodiment of the present invention;

FIG. 6 is a diagram of a distributed active transformer with switched-incapacitors that are in parallel with amplifiers in accordance with anexemplary embodiment of the present invention;

FIG. 7 is a diagram of a distributed active transformer with a low noiseamplifier in accordance with an exemplary embodiment of the presentinvention; and

FIG. 8 is a diagram of a distributed active transformer with a low noiseamplifier in accordance with another exemplary embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

In the description that follows like parts are marked throughout thespecification and drawings with the same reference numerals,respectively. The drawing figures are not necessarily to scale andcertain features may be shown in somewhat generalized or schematic formin the interest of clarity and conciseness.

FIGS. 1 AND 1A are diagrams of distributed active transformer 100 inaccordance with an exemplary embodiment of the present invention.Distributed active transformer 100 allows the number of primary sectionsin the primary winding of a distributed active transformer to bereconfigured.

Distributed active transformer 100 includes primary winding sections102A, 102B, 102C, and 102D, and secondary winding 104. Each primarywinding section has an associated push/pull amplifier pair that includesamplifiers 106A and 108A for primary winding section 102A, amplifiers106B and 108B for primary winding section 102B, amplifiers 106C and 108Cfor primary winding section 102C, and amplifiers 106D and 108D forprimary winding section 102D. The amplifiers can be implemented usingbipolar junction transistors (BJTs), metal oxide semiconductorfield-effect transistors (MOSFETs), hetero-junction bipolar transistors(HBTs), metal-semiconductor field effect transistors (MESFETs), lateraldouble-diffused metal oxide semiconductor transistors (LDMOSs),complementary MOS transistors (CMOS), or other suitable devices.Amplifier 106A drives current to the positive terminal of primarywinding section 102A, whereas amplifier 108A drives current from thenegative terminal of primary winding section 102A. The polarities of theamplifiers can be alternated to reverse the direction of current flow. Adrain voltage V_(dd) (not explicitly shown) may alternatively beprovided at a midway point, corner, or at other suitable locations oneach primary winding section to provide the current source or othersuitable configurations can be used to create time-varying current onthe primary winding sections using the push/pull amplifier pairs. Asimilar configuration is used for primary winding sections 102B, 102C,and 102D.

Each push/pull amplifier pair of each primary winding section can becontrolled so that the current flowing on the primary winding sectionalternates in direction and magnitude in a manner that creates amagnetic field that induces an electromotive force (EMF) on secondarywinding 104. The EMF causes current to flow in secondary winding 104,based on the impedance of that winding and any associated circuit. Thecurrent through the push/pull amplifier pairs can be controlled so as toadjust both the current and the voltage induced in this manner onsecondary winding 104.

Switches 110A, 110B, 110C, and 110D can be implemented as transistors,micro-electromechanical devices (MEMS), or other suitable devices, andare connected to a one amplifier out of each set of two adjacentpush/pull amplifier pairs, such that the two adjacent push/pullamplifiers can be bypassed and a new push/pull amplifier pair can becreated. As used herein, “connect” and its cognate terms such as“connects” or “connected” can refer to a connection through a conductor,a semiconducting material, or other suitable connections. In oneexemplary embodiment, amplifiers 106A and 108B are connected to switch110A, such that the amplifiers can be bypassed by closing switch 110A.In this embodiment, amplifiers 106B and 108A would then form thepush/pull amplifier pair for primary winding sections 102A and 102B.Likewise, a similar configuration can be provided for switches 110B,110C and 110D. In this regard, it should be noted that the set ofpush/pull amplifiers that the switches are connected to is differentfrom the set of push/pull amplifiers that service each primary windingsection. Nevertheless, each switch can operate to bypass one amplifierfrom a first push/pull amplifier pair and a second amplifier from asecond push/pull amplifier pair so as to result in the remainingamplifiers from those two push/pull amplifier pairs operating as apush/pull amplifier pair on a combined primary winding section.

For example, if switch 110A is closed, the power level generated bydistributed active transformer 100 is less than the power level that isgenerated for distributed active transformer 100 with all switches open.The current magnitude through secondary winding 104 will be determinedby the sum of the electromotive forces induced on the secondary by eachprimary winding section, which equals the change in flux linkages overtime (dΦ/dt) which is determined by the mutual inductance of the primaryand the secondary and the change in the current of the secondary(M*dI/dt.)

When a push-pull configuration is used with no V_(dd) points, closing asingle switch 110 results in an increased impedance for each remainingpush/pull amplifier pair that drives current through the two connectedprimary winding sections. This configuration decreases the output powerby increasing the impedance seen by the remaining amplifiers.Alternately, the winding sections can be capacitively coupled, such thatthe impedance seen by each amplifier remains the same, but where poweris controlled by turning off or switching out amplifier sections. Ineither configuration, turning off amplifiers results in a decrease inoutput power and can be used to lower the overall power dissipation ofthe amplifier.

When a push-pull configuration is used that includes V_(dd) points, witha single switch 110 closed, one quarter of the primary winding sectionwill not be carrying any current, as no current will flow between theV_(dd) points of the two connected primary winding sections.

In the described configurations, closing one switch can decrease theflux linkages between the primary and secondary windings, such that theopen loop voltage on the secondary will be decreased to fraction of themaximum open loop voltage that could be realized with all switches 110Athrough 110D open. Likewise, with two and three switches 110 closed, theopen loop voltage will drop more. Thus, distributed active transformer100 can operate in four different modes of operation—a maximum powermode with all switches 110A through 110D open, a medium-high power mode,with any one of switches 110A through 110D closed, a medium-low powermode with any two of switches 110A through 110D closed, and a low powermode with any three of switches 110A through 110D closed. The powerlevels will be a function of whether the impedance seen by eachamplifier is constant or varies as a function of the switches that areclosed, as well as other factors.

In addition to providing different power modes of operation withswitches 110A through 110D, the biasing current required for each of thebypassed amplifiers can also be decreased, such that the bias currentrequirements for distributed active transformer 100 can also becontrolled. For example, with all switches 110A through 110D open, thebias current required for each of amplifiers 106A and 108A through 106Dand 108D can be at a maximum. If switch 110A is closed, then the biascurrent required for amplifiers 106A and 108B can decrease. In thismanner, bias current requirements for distributed active transformer 100can be controlled through the use of switches 110A through 110D, wheresuitable. Likewise, the bias current for a given power level can beoptimized by determining the power level range for a given switchsetting, and using the range that provides the lowest bias current forthe expected range of operation. For example, if the expected powerlevels for the operating range of an application would fall withineither the power level range for operation of distributed activetransformer 100 with either two of switches 110 closed or three ofswitches 110 closed, then operation of distributed active transformer100 with three of switches 110 closed would satisfy the powerrequirements for the operating range while minimizing the bias currentrequired to support operation.

FIG. 1A shows an exemplary configuration of switches 120A and 120B,which can be used to connect or disconnect amplifiers 108A and 106D,respectively, from distributed active transformer 100 while allowing102A and 102D to be independently coupled or decoupled. The exemplaryconfiguration of switches 120A and 120B can be implemented at eachconnection between each primary winding section, secondary windingsections (if such sections are used), or in other suitable locations.Switches 120A and 120B thus provide additional flexibility for theconfiguration of distributed active transformer 100.

In operation, distributed active transformer 100 allows the powercapability and biasing current requirements to be controlled through theoperation of switches 110A through 110D. In this manner, additionalcontrol of the power output and power consumption of a distributedactive transformer is provided.

FIG. 2 is a diagram of distributed active transformer 200 with twoprimary windings in accordance with an exemplary embodiment of thepresent invention. Additional primary and secondary windings canlikewise be provided for additional power conversion control, eitherinternal or external to the secondary winding.

Distributed active transformer 200 includes first primary windingsections 202A, 202B, 202C, and 202D, and second primary winding 212.Secondary winding 204 is disposed between the first primary windingsections 202A through 202D and second primary winding 212. For the firstprimary winding sections, push/pull amplifiers 206A and 208A areassociated with primary winding section 202A, push/pull amplifiers 206Band 208B are associated with primary winding section 202B, push/pullamplifiers 206C and 208C are associated with primary winding section202C, and push/pull amplifiers 206D and 208D are associated with primarywinding section 202D. Likewise, push/pull amplifiers 210A and 210B areassociated with second primary winding 212, although a single driveramplifier can alternatively be used where suitable. The secondarywinding has an output 214.

Distributed active transformer 200 can operate with primary windingsections 102A through 102D active and second primary winding 212inactive. In this mode, distributed active transformer 200 can providehigher power but with increased bias current requirements. Likewise,distributed active transformer 200 can operate with primary windingsections 102A through 102D inactive and with second primary winding 212active. In this exemplary embodiment, the power delivered to output 214can be lower than the power delivered to output 214 when first primarywinding sections 202A through 202D are activated, but the bias currentrequired can be lower than the bias required with primary windingsections 202A through 202D active.

In another exemplary embodiment, the spacing between second primarywinding 212 and secondary winding 204 can be increased, so as todecrease the magnetic coupling between the primary and secondarywindings. The power loss in second primary winding 212 when it is notbeing used can thus be decreased, as well as the voltage breakdownrequirements of push/pull amplifiers 210A and 2108. Additional primarywindings can likewise be provided, depending on the power levelsrequired and the available space.

In operation, distributed active transformer 200 can be operated in afirst mode for high power with high bias current requirements byactivation of primary winding sections 202A through 202D, and in asecond mode with lower power and bias current requirements by activationof second primary winding 212. Use of a first primary winding and asecond primary winding allows the power output and bias currentrequirements for a distributed active transformer to be adjusted asneeded by switching between primaries.

FIGS. 3 AND 3A are diagrams of distributed active transformer 300A withfirst and second primary windings and compensating capacitors inaccordance with an exemplary embodiment of the present invention.Distributed active transformer 300A allows the power loss caused bycirculating currents in an unused primary winding to be mitigatedthrough the use of a switched series capacitance, as well as decreasingthe breakdown voltage imposed on the associated primary windingamplifiers.

Distributed active transformer 300A includes primary winding sections302A through 302D with associated push/pull amplifier pairs 306A and308A through 306D and 308D, respectively, and secondary winding 304 withoutput 312. Likewise, second primary winding 310 includes push/pullamplifiers 314A and 314B, which can be connected using switch 316through capacitor 318. When capacitor 318 is connected in parallel withsecond primary winding 310 through switch 316, an LC resonant circuitcan be formed with secondary winding 304. When second primary winding310 is not in use, switch 316 can be opened to take second primarywinding 310 out of resonance with secondary winding 304 and decreaselosses due to circulating currents, as well as to decrease the peakvoltage imposed on push/pull amplifiers 314A and 314B when they areinactive. In general, capacitors can be switched into and out ofwindings in other suitable configurations, to take the windings in andout of resonance with other windings.

As shown in FIG. 3A, a suitable configuration of switches and capacitorscan be used in lieu of a single switch 316 and capacitor 318, where eachswitch-capacitor pair can be controlled separately, thus allowing theresonance frequency of the secondary loop to be adjusted. In oneexemplary embodiment, this combination can be used to adjust the centerfrequency of a power amplifier so as to achieve a flat gain andefficiency response across multiple frequency bands or channels, toaccount for manufacturing process variations, to account for temperaturevariations, or for other suitable purposes.

FIG. 4 is a diagram of distributed active transformer 300B with firstand second primary windings and compensating capacitors in accordancewith an exemplary embodiment of the present invention. Distributedactive transformer 300B allows the power loss caused by circulatingcurrents in an unused primary winding to be mitigated through the use ofswitched capacitors, as well as decreasing the breakdown voltage imposedon the associated primary winding amplifiers.

Distributed active transformer 300B includes primary winding sections302A through 302D with associated push/pull amplifier pairs 306A and308A through 306D and 308D, respectively, with secondary winding 304 andoutput 312. Likewise, second primary winding 310 includes push/pullamplifiers 314A and 314B, which can be connected using switches 316through capacitors 318. When capacitors 318 are connected to secondprimary winding 310 through switches 316, an LC resonant circuit iscreated with secondary winding 304. When second primary winding 310 isnot in use, switches 316 can be opened to take second primary winding310 out of resonance with secondary winding 304 and decrease losses dueto circulating currents, as well as to decrease the peak voltage imposedon push/pull amplifiers 314A and 314B when they are inactive.

FIG. 5 is a diagram of distributed active transformer 400 with impedancetransformation ratio correction and resonance frequency selection inaccordance with an exemplary embodiment of the present invention.Distributed active transformer 400 includes primary winding sections402A through 402D with associated push/pull amplifiers 406A and 408Athrough 406D and 408D, respectively. Switches 418A through 418D areconnected in series with capacitors 416A through 416D, respectively.Output 410 of secondary winding 404 includes switch 414 and capacitor412 for impedance transformation ratio control. Alternatively, switch414 and capacitor 412 can be omitted, such as where it is desirable onlyto allow the resonance frequency of distributed active transformer 400to be controlled. Likewise, a suitable configuration of switches andcapacitors can be used in lieu of a single switch 414 and capacitor 412,where each switch-capacitor pair can be controlled separately, thusallowing the resonance frequency of the secondary loop to be adjusted.

In this exemplary embodiment, the power operation mode of distributedactive transformer 400 can be controlled, such as by closing one or moreof switches 418A through 418D, so as to insert capacitors 416A through416D in series with primary winding sections 402A through 402D. In thismanner, a series LC circuit is created to compensate for leakageinductance between the primary winding sections 402A through 402D andsecondary winding 404. Thus, by placing one or more of capacitors 416Athrough 416D in series with primary winding sections 402A though 402D,the maximum output power is decreased, but the bias current required toachieve a gain level is also decreased. Alternatively, if capacitor 412is placed in parallel across the load by closing switch 414 tocompensate for this leakage inductance, then the impedancetransformation ratio is increased, which increases the maximum outputpower but which also increases the bias current requirements.

In addition, the resonant frequency of distributed active transformer400 can be adjusted for a particular frequency of operation by switchingin capacitors 416A through 416D. In this manner, the efficiency andpower output by distributed active transformer 400 can be optimized fora desired frequency of operation by configuring it for resonance at thatfrequency. Thus, depending on the sizes of the capacitors, distributedactive transformer 400 can be operated in a first mode either with orwithout switch 414 and capacitor 412 to change the impedancetransformation ratio by compensating for winding leakage inductance, ina second mode without switch 414 and capacitor 412 to change theresonant frequency of distributed active transformer 400, or in bothmodes simultaneously. Likewise, a suitable configuration of switches andcapacitors can be used in lieu of switches 418 and capacitors 416, whereeach switch-capacitor pair can be controlled separately, thus allowingthe resonance frequency of the primary loop to be adjusted.

FIG. 6 is a diagram of distributed active transformer 500 withswitched-in capacitors that are in parallel with amplifiers 506A and508A through 506D and 508D, in accordance with an exemplary embodimentof the present invention. Distributed active transformer 500 includesprimary windings sections 502A through 502D with associated push/pullamplifiers 506A and 508A through 506D and 508D, respectively. Switchpairs 518A through 518D are connected in series with capacitor pairs516A through 516D, respectively. Output 510 of secondary winding 504includes switch 514 and capacitor 512 for impedance transformation ratiocontrol. Alternatively, switch 514 and capacitor 512 can be omitted,such as where it is desirable to allow the resonance frequency ofdistributed active transformer 500 to be controlled.

In this exemplary embodiment, the power operation mode of distributedactive transformer 500 can be controlled, such as by closing one or moreof switch pairs 518A through 518D, so as to insert capacitor pairs 516Athrough 516D in series with primary winding sections 502A through 502D.In this manner, a series LC circuit is provided to compensate forleakage inductance between the primary winding sections 502A through502D and secondary winding 504. Thus, by placing one or more ofcapacitor pairs 516A through 516D in series with primary windingsections 502A though 502D, the maximum output power is decreased, butthe bias current required to achieve a gain level is also reduced.Alternatively, if capacitor 512 is placed in parallel across the load byclosing switch 514 to compensate for this leakage inductance, then theimpedance transformation ratio is increased, which increases the maximumoutput power but which also increases the bias current requirements.

In addition, the resonant frequency of distributed active transformer500 can be adjusted for a particular frequency of operation by switchingin capacitor pairs 516A through 516D. In this manner, the efficiency andpower output of distributed active transformer 500 can be optimized fora desired frequency of operation by placing it in resonance for thatfrequency. Thus, depending on the sizes of the capacitors, distributedactive transformer 500 can be operated in a first mode either with orwithout switch 514 and capacitor 512 to change the impedancetransformation ratio by compensating for winding leakage inductance, ina second mode without switch 514 and capacitor 512 to change theresonant frequency of distributed active transformer 500, or in bothmodes simultaneously.

FIG. 7 is a diagram of distributed active transformer 600 integratedwith a low noise amplifier in accordance with an exemplary embodiment ofthe present invention.

In addition to the primary and secondary windings and associatedpush/pull amplifiers previously described, distributed activetransformer 600 includes a low noise amplifier 614 and associated switch612. When switch 612 is closed, as shown, a transmitted signal can beprovided by modulating the input through push/pull amplifiers 606A and608A through 606D and 608D. When switch 612 is opened and push/pullamplifier pairs 606A and 608A through 606D and 608D are not operated, areceived signal can be fed through an inductor coil formed by thesecondary winding of distributed active transformer 600, and low noiseamplifier 614 can be used to process the signal. In this manner,integration of low noise amplifier 614 with switch 612 through asingle-ended output of distributed active transformer 600 allows areceiver/transmitter architecture to be implemented. In one exemplaryembodiment, distributed active transformer 600 can be used in place of atransmit switch in a transceiver, or for other suitable applications.

FIG. 8 is a diagram of distributed active transformer 700 with a lownoise amplifier in accordance with another exemplary embodiment of thepresent invention. Although a low noise amplifier is shown, any suitabledevice can be used, including but not limited to a mixer, a transceiver,a filter, and a digital to analog converter.

In addition to the primary and secondary winding structures andassociated push/pull amplifiers previously described, distributed activetransformer 700 includes a split secondary winding 704 with switches710A and 710B connected to low noise amplifier 712. Distributed activetransformer 700 can be operated in a first transmit mode with switches710A and 710B closed, as shown, and in a second receive mode withswitches 710A and 710B open. When switches 710A and 710B are open, lownoise amplifier 712 can be used to amplify a signal received at input714. When switches 710A and 710B are closed, primary winding sections702A through 702D of distributed active transformer 700 can be driven bypush/pull amplifiers 706A and 708A through 706D and 708D, respectively,so that an input signal can be amplified and provided for transmissionat input 714.

Although exemplary embodiments of the system and method of the presentinvention has been described in detail herein, those skilled in the artwill also recognize that various substitutions and modifications can bemade to the systems and methods without departing from the scope andspirit of the appended claims.

1. A distributed active transformer comprising: a primary winding havingone or more pairs of amplifiers; a secondary winding disposed adjacentto the primary winding; and wherein the primary winding and thesecondary winding are disposed on a semiconductor substrate.
 2. Thedistributed active transformer of claim 1 further comprising one or moreswitches that can be used to bypass one or more of the amplifiers. 3.The distributed active transformer of claim 1 wherein the primarywinding further comprises: two or more sections, wherein each sectionterminates in one of the pairs of amplifiers; and a switch connected toone of the amplifiers from the first section and to one of theamplifiers from the second section, wherein the switch can be used tobypass the amplifier from the first section and the amplifier from thesecond section so as to combine two of the sections into a singlesection. 4-17. (canceled)
 18. A distributed active transformercomprising: a primary winding having two or more sections, where eachsection has a pair of push/pull amplifiers; a secondary winding disposedadjacent to the primary winding; and wherein the primary winding and thesecondary winding are disposed on a semiconductor substrate.
 19. Thedistributed active transformer of claim 18 wherein the push/pullamplifiers of each section can be independently controlled.
 20. Thedistributed active transformer of claim 18 further comprising a secondprimary winding having one or more sets of push/pull amplifiers disposedadjacent to the secondary winding.
 21. A system for amplifying a signalcomprising: a distributed active transformer having a primary and asecondary winding; and a low noise amplifier coupled to the secondarywinding of the distributed active transformer by a switch.
 22. Thesystem of claim 21 wherein the system operates in a receive mode whenthe switch is opened and in a transmit mode when the switch is closed.23. The system of claim 21 wherein the low noise amplifier is coupled tothe distributed active transformer when the switch is opened and the lownoise amplifier is bypassed when the switch is closed.
 24. The system ofclaim 21 wherein the low noise amplifier comprises a differential lownoise amplifier having a first input and a second input, and thesecondary winding further comprises a first section coupled to the firstinput through the switch and a second section coupled to the secondinput through a second switch.
 25. The system of claim 24 wherein thesystem operates in a receive mode when the switches are opened and in atransmit mode when the switches are closed.
 26. The system of claim 24wherein the low noise amplifier is coupled to the distributed activetransformer when the switches are opened and the low noise amplifier isbypassed when the switches are closed.
 27. The distributed activetransformer of claim 18 further comprising one or more switches that canbe used to bypass one or more of the push/pull amplifiers.
 28. Thedistributed active transformer of claim 18 wherein the primary windingfurther comprises: two or more sections, wherein each section terminatesin one of the pairs of push/pull amplifiers; and a switch connected toone of the amplifiers from the first section and to one of theamplifiers from the second section, wherein the switch can be used tobypass the amplifier from the first section and the amplifier from thesecond section so as to combine two of the sections into a singlesection.
 29. The distributed active transformer of claim 1 furthercomprising a switch, wherein the distributed active transformer operatesin a receive mode when the switch is opened and in a transmit mode whenthe switch is closed.
 30. The distributed active transformer of claim 1further comprising a low noise amplifier coupled to the distributedactive transformer when a switch is opened and the low noise amplifieris bypassed when the switch is closed.
 31. The distributed activetransformer of claim 30 wherein the low noise amplifier comprises adifferential low noise amplifier having a first input and a secondinput, and the secondary winding further comprises a first part coupledto the first input through the switch and a second part coupled to thesecond input through a second switch.
 32. The distributed activetransformer of claim 31 configured to operate in a receive mode when theswitches are opened and in a transmit mode when the switches are closed.33. The distributed active transformer of claim 31 wherein the low noiseamplifier is coupled to the distributed active transformer when theswitches are opened and the low noise amplifier is bypassed when theswitches are closed.
 34. The distributed active transformer of claim 1wherein the amplifiers can be independently controlled.
 35. Thedistributed active transformer of claim 1 further comprising a secondprimary winding having one or more amplifiers, wherein the secondprimary winding is disposed adjacent to the secondary winding.
 36. Thedistributed active transformer of claim 18 further comprising a switch,wherein the distributed active transformer operates in a receive modewhen the switch is opened and in a transmit mode when the switch isclosed.
 37. The distributed active transformer of claim 18 furthercomprising a low noise amplifier coupled to the distributed activetransformer when a switch is opened and the low noise amplifier isbypassed when the switch is closed.
 38. The distributed activetransformer of claim 37 wherein the low noise amplifier comprises adifferential low noise amplifier having a first input and a secondinput, and the secondary winding further comprises a first part coupledto the first input through the switch and a second part coupled to thesecond input through a second switch.
 39. The distributed activetransformer of claim 38 configured to operate in a receive mode when theswitches are opened and in a transmit mode when the switches are closed.40. The distributed active transformer of claim 38 wherein the low noiseamplifier is coupled to the distributed active transformer when theswitches are opened and the low noise amplifier is bypassed when theswitches are closed.
 41. The system of claim 21 wherein the primarywinding comprises a plurality of amplifiers, and each of the amplifierscan be independently controlled.
 42. The system of claim 21 furthercomprising a second primary winding having one or more amplifiers, thesecond primary winding disposed adjacent to the secondary winding.